The present invention is directed to a system and method for controlling an automatic transmission including controlling transmission hydraulic pressure during ratio changes.
Mechanical throttle control systems use airflow as the primary control parameter in controlling engine or powertrain output. The airflow is controlled by a throttle valve in the intake which is mechanically linked to a throttle pedal. As such, many powertrain control parameters, including automatic transmission hydraulic pressure control, were traditionally based on, or indexed by, the throttle valve position.
Electronic airflow control systems, such as variable cam timing systems and electronic throttle control systems, replace the traditional mechanical throttle cable system with an xe2x80x9celectronic linkagexe2x80x9d provided by sensors and actuators in communication with an electronic controller. This increases the control authority of the electronic controller and allows the airflow to be controlled independently of the accelerator pedal position. As such, the throttle valve position is no longer necessarily indicative of the requested or desired powertrain output.
It is an object of the present invention to provide a system and method for controlling hydraulic pressure within an automatic transmission during a ratio change based on a desired powertrain output, such as engine torque, wheel torque, wheel power, or tractive effort.
In carrying out the above object and other objects, advantages, and features of the present invention, a system and method for controlling a vehicular powertrain including an automatic transmission having a plurality of selectable input to output ratios, include determining a value representing requested powertrain output, determining a rotational speed representing current operating conditions, generating a command to initiate a ratio change in the automatic transmission, determining a dynamic pressure for the automatic transmission during the ratio change based on the requested powertrain output and the rotational speed, and using the dynamic pressure to control the actuation pressure of the automatic transmission. In one embodiment, a performance adder is determined based on the requested powertrain output and added to the dynamic pressure. Powertrain output may be represented by various parameters including engine torque, wheel torque, wheel power, and tractive effort, for example. Likewise, depending upon the particular application, the rotational speed may represent vehicle speed, output shaft speed, wheel speed, or the like.
The present invention provides a number of advantages over prior art control strategies. For example, the present invention provides a modular control structure where hydraulic pressure control during ratio changes is based on powertrain output, such as requested wheel torque, rather than throttle position. As such, the control strategy of the present invention may be easily adapted to new engine technologies such as lean burn, variable cam timing, and direct injection. Dynamic hydraulic pressure control which is independent of throttle valve position allows increased authority of control of the throttle valve such that it can be nearly wide open without affecting various other vehicle operating parameters, including transmission hydraulic pressure control.
In a preferred embodiment, dynamic electronic pressure control based on wheel torque and vehicle speed provides better compensation at higher altitudes (lower barometric pressure) while facilitating calibration of the pressure control in the same domain as the shift schedules.
The above advantages and other advantages, objects, and features of the present invention, will be readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.